JP2000198433A - Method and device for controlling braking action in at least one wheel brake of four-wheel drive automobile - Google Patents

Abstract

PROBLEM TO BE SOLVED: To suppress vibration of a drive line by measuring a first rotating speed signal indicating the wheel rotating speed of a front axle and a second rotating speed signal indicating the wheel rotating speed of a rear axle, determining the difference between the first and second rotating speed signals, and controlling braking action as a function of determined difference. SOLUTION: Wheel rotating speed sensors 101VL, 101VR, 101HL, 101HR measure wheel rotating speed V-VL, V-VR, V-HL, V-HR. Reference speed Vref indicating the longitudinal speed of a vehicle is formed from the wheel rotating speed in a block 104, and a friction coefficient μ of the travel road surface is formed in a block 103. In a block 102, the value DVaxle indicating the grade of axle vibration is determined by an expression: Vaxle=(V-VL+V- VR)-(V-HL+V-HR). Brake pressure is lowered to lower the value DVaxle.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method and a device for controlling the braking action of at least one wheel brake of a four-wheel drive vehicle.

[0002]

2. Description of the Related Art Antilock control systems (ABS systems) are known in various ways. Here, for example, the document “Bos
ch Technical Report, Vol. 7 (1980), No. 2. In such an anti-lock control device, the brake device for the vehicle wheels is operated such that the brake pressure changes as a function of the instability value. In this case, this instability value is formed as a function of the detected wheel movement, generally the wheel rotational speed. In particular, this instability value is determined by the momentary wheel circumferential deceleration or wheel circumferential acceleration,
Combination with brake slip. A correction of such an instability value is known from DE-A-196 114 91.

From DE-A-195 16 120 (US Pat. No. 5,556,174), especially in all-wheel-drive vehicles, during the ABS control process, vibrations at the drive wheels due to the elasticity between the engine and the wheels occur at the drive wheels. It is known that this can happen. To detect this vibration,
The speed in the differential gear of the drive axle is determined. Next, it is determined whether a signal having a frequency lying within the range determined by the vibration of the drive train is superimposed on this speed. In response to the detected drive train vibration, the operating time of the brake pressure controller is adjusted such that the drive train vibration is reduced.

Furthermore, vehicles are known in which not only the wheels of the rear axle but also the wheels of the front axle are driven. Such 4
In wheel drive vehicles, the differential may be at least partially locked. In four-wheel drive vehicles, axle vibrations can occur during the ABS braking process, especially when the differential is at least partially locked.

[0005]

SUMMARY OF THE INVENTION It is an object of the present invention to effectively suppress vibration in a drive train of a four-wheel drive vehicle.

[0006]

SUMMARY OF THE INVENTION The present invention provides at least one
The present invention relates to a method and a device for controlling the braking action of at least one wheel brake of a four-wheel drive vehicle having two rear and front axles. In this case, a first speed signal representing the rotational speed of the wheels on the front axle and a second speed signal representing the rotational speed of the wheels on the rear axle are measured. Next, the difference between the first and second speed signals is determined, and the braking action is controlled as a function of the determined difference.

In this case, in particular, a value representing the road surface condition, in particular the coefficient of friction of the road surface, is determined, and when the determined value falls below a threshold value, the control of the braking action is determined by the determined difference. Designed to be performed as a function. In this case, it may be provided that the control of the braking action is performed only as a function of the determined difference when the determined value falls below a threshold value.

In a particularly advantageous embodiment of the invention, the motor vehicle is designed to have at least a partially lockable differential in the drive train. When the differential is partially locked, the control of the braking action according to the invention takes place as a function of the determined difference.

As mentioned at the outset, in a four-wheel drive vehicle with a lockable differential, the connection between the drive train and the drive wheels during the anti-lock control process, especially due to the tightening of the wheels, occurs. May generate axle vibration. This occurs in particular on road surfaces (ice or snow) which have a relatively low coefficient of friction. This axle vibration can have a detrimental effect on the operation of the antilock control device (ABS) which prevents the locking tendency present on the wheels by brake engagement. Furthermore, this axle vibration
In the course of braking on a road surface with a low or moderate coefficient of friction (ice or snow), the riding comfort and the braking performance are also adversely affected.

For the ABS control process, it is necessary to determine a so-called reference speed, which represents the longitudinal speed of the vehicle. This is generally done based on the measured wheel speed. By high frequency axle vibration and resonance with it,
The determination of the reference speed, and thus the overall ABS control process, can be severely disrupted. According to the present invention, the magnitude of the axle vibration is determined according to the wheel speed (V_VL, V_VR, V
_HL, V_HR).

[0011]

(Equation 1)

It is measured by the formation of The means for preventing axle vibration according to the present invention is suitable for effectively preventing or attenuating the vibration and thus for preventing or reducing the magnitude of this vibration in order to maintain the ABS control overall. I have.

The determined difference DVaxle is at least one.
Below and / or above one threshold,
The control of the braking action according to the invention is determined by the determined difference DV.
It is particularly advantageous to do this as a function of axle. In this case, only when the determined difference DVaxle falls below and / or exceeds at least one threshold value,
The control of the braking action may be designed to take place as a function of the determined difference.

In the hydraulic brake system, the braking action is controlled by supplying brake fluid to the wheel brake and discharging brake fluid from the wheel brake. To this end, operable inlet and outlet valves are generally provided. As soon as the axle vibrations are measured with the value DVaxle, the prevention, damping or reduction of the axle vibrations according to the invention takes place by the provision of a suitable operation of the inlet or outlet valve with respect to the brake fluid, whereby , The value DVaxle exceeds a predetermined positive threshold,
Or immediately below a predetermined negative threshold, the value DVa
xle is reduced. In this case, two methods are considered.

A first method consists in that the control of the braking action is performed as a function of the determined difference DVaxle, such that the increase in the braking action takes place at the higher rotational speed of the vehicle axle.

A second method consists in that the control of the braking action is performed as a function of the determined difference DVaxle such that a reduction in the braking action takes place on the lower axle of the vehicle.

As described at the outset, the change in the braking action in the ABS system is generally performed as a function of the so-called instability value. The operation of the inlet and outlet valves for brake fluid takes place as a function of this instability value.
Here, in the presence of an ABS device, the instability value is modified as a function of the value DVaxle in order to control the braking action according to the invention as a function of the vibration value DVaxle (increase or decrease of the brake pressure).

It is an object of the invention to keep or reduce the axle vibration represented by the value DVaxle so that problems due to axle vibration during the ABS control process are not expected. In this case, it is preferable, for safety reasons, that the braking action or the reduction of the braking pressure takes place only as a function of the DVaxle.

[0019]

FIG. 1 is a block circuit diagram showing the whole of the present invention. In this case, the brake control on the right rear wheel of the vehicle is shown schematically.

Wheel speed sensors 101VL, 101V
R, 101HL and 101HR are wheel rotation speeds, that is, wheel rotation speeds V_VL, V_VR, V_HL and V_
Measure HR. In block 104, a reference speed Vref representing the vehicle longitudinal speed is formed from the wheel speed in a known manner. In block 103, the coefficient of friction μ of the road surface is formed. This takes place, as is known, as a function of the wheel speed and possibly also other values.

At block 105, the instability value IS
S is formed. In a typical anti-lock control device, block 105 determines that the instability value ISS is

[0022]

(Equation 2)

It may be designed to be formed by: In this case, the values K1, K2 and K3 indicate the amplification factor, and the value ARS means an offset with respect to the control threshold. In this case, the wheel deceleration ahl and the brake slip λ are included as negative values.

Essentially, the instability value thus formed is used to interrogate an instability condition in normal ABS control, which determines an operating point for normal antilock control. . Therefore,
Two regions are distinguished (see blocks 108, 109 and 110). That is, ISS <SW (eg, SW = 0): (rear right) wheel is unstable, and (rear right) wheel brake pressure decreases (block 109: PHR ↓).

ISS ≧ SW (for example, SW = 0): (Rear right) Wheel is stable, (Rear right) Wheel brake pressure increases (Block 110: PHR #).

It is pointed out here again that the embodiment described here illustrates the invention by brake application to the right rear wheel brake (index: HR).

Further, it should be pointed out that the above determination of instability values represents only one of a number of methods. In particular, in brake control and / or propulsion control operating on torque, the instability value to be adjusted according to the invention may be indicative of wheel torque.

In block 102, a value DVaxle representing the magnitude of axle vibration is determined by the following equation.

[0029]

(Equation 3)

Signal 4WD output from block 107
Gives whether there is a four-wheel drive operation with the differential locked.

The correction of the instability value ISS according to the invention in block 106 will be explained with reference to the flow chart shown in FIG. 2 for the example of the right rear wheel brake.

In FIG. 2, following the start step 21, in a step 22, the above-mentioned input value DVax
le, 4WD, μ and ISS are read.

In step 23, an inquiry is made as to whether there is a four-wheel drive operation with the differential locked. If this is not the case, end step 30
Migrated directly to

When such a four-wheel drive motion exists,
In step 24, an inquiry is made as to whether the friction coefficient μ is below a settable threshold value SW1.
If this is not the case, the vehicle is traveling on a slippery road surface and a direct transition is made to end step 30.

However, if the road surface has a low to moderate coefficient of friction (eg, ice or snow),
In step 25, it is determined whether the wheel to be controlled is a front axle wheel or a rear axle wheel.

To explain steps 26, 27, 28 and 29, reference should also be made to FIG.

When the right rear wheel is noticed as in this example, it is inquired in step 27 whether the axle vibration value DVaxle is lower than the positive threshold value SWhigh. If this is affirmative (regions A and B in FIG. 3)
Or C), which is due to whether the axle vibration DVaxle is not very large (regions B and C) or whether the wheels of the rear axle are on average rotating faster than the wheels of the front axle (region A) Means either. As mentioned at the outset, increasing the brake pressure at the rear axle wheels does indeed reduce the value DVaxle, but in this embodiment the brake pressure should merely be reduced in order to reduce the value DVaxle. is there. For this reason, if the inquiry result in step 27 is affirmative "Y", no correction of the instability value ISS should be made at the rear axle. Therefore, end step 3
Migrated directly to 0.

However, if the target wheel is located on the right front axle, in step 26, the axle vibration value DV
It is queried whether axle exceeds a negative threshold value SWlow. If this is the case (regions B, C or D in FIG. 3), this means that the axle vibration DVaxle is not very large (regions B and C) or that the wheels of the front axle are on average more essential than the wheels of the rear axle. It means that the target is rotating faster (region D).
As mentioned at the outset, increasing the brake pressure at the wheels of the front axle certainly decreases the value DVaxle, but in this embodiment the brake pressure is reduced to reduce the value DVaxle. For this reason,
If the result of the inquiry in step 26 is affirmative "Y", no correction of the instability value ISS should be made in the front axle. Therefore, the process directly proceeds to the end step 30.

If, however, the result of the inquiry at steps 26 (front axle) and 28 (rear axle) is negative "N", the value DVaxle is set to the area A (front axle) or the area D
(Rear axle). Here, in step 28, the correction value K is set as a function F of the axle vibration value DVaxle.
OR is formed. Next, in step 29, the instability value ISS is reduced by the correction value KOR. This function may be a function of other data. Thus, the value KOR may be selected, for example, as a function of the axle.

Looking at the above blocks 108, 109 and 110 of FIG. 1, the reduction in the value ISS indicates that the brake pressure drop (block 109) was reduced faster than when there was no reduction that is a function of DVaxle. means. That is, in the case of the wheels of the front axle in the area A (FIG. 3), the brake pressure on the front axle is reduced more quickly. In the case of the wheels of the rear axle, the brake pressure at the rear axle is reduced earlier in region D (FIG. 3).

After the end step 30, the program shown in FIG. 2 is started again. That is, according to the above embodiment of the invention, the instability criterion or stability criterion of the normal antilock control is modified as a function of the magnitude of the axle vibration. In this way, a brake pressure drop is achieved on an axle with slower rotating wheels, whereby an increase in wheel speed on this axle is achieved.
This is because the vehicle exists on a traveling road surface having a low friction coefficient in the four-wheel drive operation, and the axle vibration is within a predetermined region [SWl
ow, SWhigh].

[Brief description of the drawings]

FIG. 1 is a block circuit diagram showing the whole of the present invention.

FIG. 2 is a flowchart showing the functions of the present invention.

FIG. 3 is an explanatory diagram of a threshold value for axle vibration.

[Explanation of symbols]

101VL, 101VR, 101HL, 101HR Wheel speed sensor 102 Axle vibration value (DVaxle) determination block 103 Friction coefficient (μ) formation block 104 Reference speed (Vref) formation block 105 Instability value (ISS) formation block 106 Instability value ( ISS) Modification block 107 4WD formation block 108 Comparison block 109 Right rear wheel brake pressure drop 110 Right rear wheel brake pressure rise ahl Wheel deceleration ARS Offset to control threshold DVaxle Axle vibration value F Function to form correction value HA Rear axle ISS Instability value KOR Correction value K1, K2, K3 Amplification coefficient SW Instability value threshold value SWhigh Instability value positive threshold value SWlow Instability value negative threshold value SW1 μ threshold value VA Axle V ef reference speed (longitudinal velocity of the vehicle) V_VL, V_VR, V_HL, V_HR wheel rotational speed (wheel speed) signal λ brake slip μ friction coefficient indicating the four-wheel drive operation 4WD differential gearing is locked

 ──────────────────────────────────────────────────続 き Continuation of the front page (72) Inventor John Gazza 48504, Michigan, USA, Frank Street, 726 (72) Inventor Michael Lindemann, 48034, Michigan, USA, Southfield, Poinciana Street 22150 (72) Inventor John W. Liu 91855, West Haven Road, San Marino, California, USA 1855

Claims (10)

[Claims] 1. A method for controlling a braking action in at least one wheel brake of a four-wheel drive vehicle having at least one rear axle and one front axle, the method comprising: indicating a rotational speed of a wheel on the front axle. 1 speed signal (V _- VL + V _- VR) and a second speed signal (V _- HL + V _- H) indicating the rotation speed of the wheels on the rear axle.
R) and a difference (DVaxe) between the first and second rotational speed signals.
l) is determined and said braking action is controlled as a function of a determined difference (DVaxel). 2. A value (μ) indicating a road surface condition, in particular, a friction coefficient of the road surface is determined, and when the determined value (μ) falls below a threshold value, the control of the braking action is determined. 2. The method according to claim 1, wherein the step is performed as a function of the difference (DVaxel). 3. The vehicle has a differential gear at least partially lockable in a drive train;
2. The method according to claim 1, wherein the control of the braking action is performed as a function of the determined difference (DVaxel) when the differential gear is at least partially locked. 4. When the determined difference (DVaxel) is at least below and above a threshold value, the control of the braking action is controlled by the determined difference (DVaxel).
2. The method of claim 1 wherein the method is performed as a function of (Vaxel). 5. The method of claim 1, wherein the control of the braking action is performed as a function of a determined difference (DVaxel) such that the increase of the braking action is performed on a vehicle axle exhibiting a higher rotational speed. 2. The method according to claim 1, wherein the reduction is performed such that the reduction is performed for a vehicle axle exhibiting a lower rotational speed. 6. A rotational speed signal indicative of the rotational movement of the wheel is measured, and as a function of the measured rotational speed signal, an instability for at least one wheel is determined, in particular when the wheel is prone to locking. The control of the braking action is performed as a function of the determined instability, and the control of the braking action is determined by the determined difference (DVaxe
2. The method according to claim 1, wherein the determined instability is modified as a function of l) as a function of the determined difference (DVaxel). 7. A control device for a braking action in at least one wheel brake of a four-wheel drive vehicle having at least one rear axle and one front axle, the control device indicating a rotational speed of a wheel on the front axle. 1 speed signal (V _- VL + V _- VR) and a second speed signal (V _- HL + V _- H) indicating the rotation speed of the wheels on the rear axle.
R) and a difference (DVaxe) between the first and second rotational speed signals.
I) is determined, and the braking action is controlled as a function of the determined difference (DVaxel). 8. A value (μ) indicating a road surface condition, particularly a friction coefficient of the road surface, is determined, and when the determined value (μ) falls below a threshold value, the control of the braking action is determined. Carried out as a function of the difference (DVaxel), and the vehicle has a differential gear in the drive train that is at least partially lockable, when the differential gear is at least partially locked. And / or performing the control of the braking action as a function of the determined difference (DVaxel).
Equipment. 9. The control of the braking action as a function of the determined difference (DVaxel) when the determined difference (DVaxel) is at least below and / or above a threshold value. 8. The apparatus of claim 7, wherein said step is performed. 10. The control of the braking action as a function of a determined difference (DVaxel), such that the increase of the braking action is performed on a vehicle axle exhibiting a higher rotational speed, or the braking is performed. 8. The device according to claim 7, wherein the effect reduction is performed such that it is performed for a vehicle axle exhibiting a lower rotational speed.